In recent years the need for alternatives to fossil fuels has become painfully apparent. Solar energy offers a particularly attractive source of energy because it is non-polluting and generally available. Solar energy is particularly suitable for heating homes and other structures. Because the supply of solar energy is periodic by nature, its use as a constant energy source depends on a system to store the energy during periods of high solar radiation. Several types of systems to store the insolation have been developed in the past. They have generally used water, crushed rock, concrete, or earth as a thermal storage medium. To reduce the bulk and increase the storage efficiency of these thermal storage reservoirs, systems based on the use of a phase change material have been developed because of the large quantities of heat absorbed as latent heat of fusion at constant temperature during melting or freezing. Such materials can store an enormous quantity of heat relative to their mass. They thereby reduce the physical size and weight of the heat reservoir.
One configuration for encapsulating phase change materials is in the form of cylindrical columns called energy rods. These rods have a low surface area to volume ratio and consequently they do not collect or distribute heat well. The heat storage tray system, the invention described below, allows for an improved surface to volume ratio for both collecting and redistributing heat. It also takes up less floor space and allows for greater view than energy rods used in an indirect gain design. The tray system also provides less temperature swing in the room than energy rods used in a direct gain design. The rods often have a tendency to buckle and shift position due to thermal expansion and contraction.
Another configuration for using energy absorbing, phase change materials is in generally planar ceiling tiles. Such tiles are primarily used for absorbing excess heat during the day and radiating the heat during the evening. It has been found that if sunlight passing through a window is reflected directly to heat absorbing panels on the ceiling, the space adjacent to the window becomes unuseable for two reasons. First, the path of the light, typically reflected by a type of Venetian blind, cannot be blocked as it passes toward the celing panels. Second, if people walk near the window they may have the sunlight reflected directly into their eyes causing extreme visual discomfort. A further problem is that the physical adjustments of the blinds is extremely critical so the performance of the system can be greatly impaired by the user.
Another type of solar heating apparatus includes a Venetian blind having slats which are reflective on one surface and absorptive on the opposite surface. By manipulating the angle of the slats, sunlight can be reflected back to the window during the summer or absorbed on the absorptive surface during the winter to heat the room. With such a system the angular adjustment of the Venetian blind is critical; thus the possibility for maladjustment is present. Also such movable apparatus can be relatively costly to produce and maintain. Since such a system demands constant adjustment, user acceptance may be low. Also when is it desired that sunlight be reflected back through the window, the view through the window is drastically reduced or even eliminated. Further, the absorptive surfaces on such Venetian blinds have a low thermal storage capacity; therefore such systems lack the ability to effectively dampen temperature fluctuations within the room because they cannot store daytime heat for nighttime redistribution to the room. In these systems useful heat must often be rejected because of room overheating.